Satgen 394  Satellites in Shadow by GM4IHJ  (BID SGEN394)    12 Oct 96

Over the next few months , the RadioSport satellites and Oscar 10 will
perform highly individual dances in and out of sunlight.

Date          31/10          30/11   1996     1/1   1997     31/1 
       .........l..............l...............l...............l
Ao10 never goes into shadow behind the earth until end of period
RS10   ----in shadow part of every orbit--clear----shadow------
RS12   clear  ---in shadow part of every orbit----------clear--
RS15   -shadow-- in the clear in clear--in shadow every orbit--

As the rough figure shows Ao10 does not go into shadow in this time
frame, but RS10 and RS12 are only very rarely in continuous sunlight
By contrast RS15 has a long clear period in sunlight.

The reasons for these differences in behaviour, lie in the satellites
orbits. Ao10 is much higher than the other satellite and therefore
sees the sun from much further around the earth.Equally important its
right ascension ( orbit plane alignment with the stars) changes very
slowly. Which is lucky, because when it goes into shadow its power
supplies fail immediately.

RS10 and RS12 have only short periods of a few days when no orbits go
into shadow. They are at low altitude and hence have to be much closer
round the earth to the Sun , in order to see it. They also have an
orbit plane alignment which keeps them in a bad sun angle for long
periods, and their high orbit inclination angle (82degs) means they
spend a lot of time in or near the polar darkness far from the sunny
equatorial regions.

RS15 is by contrast more fortunate . It is higher than RS10 and 12,
and therefore sees more sunlight. Its orbit inclination of (62degs)
keeps it near the equatorial belt but combined with its big footprint
angle allows it to see the polar regions and hence the Sun over the
pole when it is in the same hemisphere (ie when both it and the sun
have +ve latitude, or both have -ve latitude). Added to this its right
ascension alignment with the stars changes twice as fast as that of
RS10 or 12, so it does not linger for long periods at bad sun angles.

All of which is lucky for RS15 and Ao10 . Seeing a lot of sunlight
compensates to some extent for their power supply difficulties.
Although both fade and become non operational from time to time. Not
so RS10 and 12 which have soldiered on for 9 and 6 years respectively
giving excellent service despite their harsh in and out of shadow
routine. How long RS10 and 12 will last is of course uncertain. Some
authorities hold that going into shadow regularly, keeps the battery
in good shape. More use is better than no use. As was demonstrated by
the old Oscars which went into high constant sunlight sun synchronous
orbits ( no battery usage), were they stayed for 5 years or so before
slipping slowly out of synch with the Sun at which point their
underworked batteries soon gave up and failed. Lets hope RS10 and RS12
last for a long time to come as correspondence here to IHJ suggests a
lot of Radio Amateurs enjoy using them.